If you can fly via the UK, you could also check Virgin Atlantic. They fly LGW-HAV, and I think that Virgin Holidays offer packages to Cuba also.
There's also Mexicana from MEX, and Mexicana's Click from CUN. Though the fares to Cuba from Mexico aren't usually that low, CUN-HAV might be an option if you could get something cheap to CUN from Europe.
If this is your first visit to Cuba, one thing I'd suggest is that it might be worth paying a little extra for a ticket that gives you flexibility to change your return date. Cuba is different, and a fair number of people who visit the island for the first time either discover that they hate the place and want to leave sooner than they had planned, or fall head over heels in love with it and want to stay longer.
If you decide on AF, you should post your question about the 744/77W on the AF forum. Many posters there are sure to be able to tell you all about the ins and outs of both, and you're sure to get a quick answer.
